The surface components of host cells which specifically interact with paramyxoviruses during the early stage of viral infection will be studied. Emphasis will be on the identification of the chemical nature of the receptor, i.e., if glycoproteins in addition to glycolipids can function as receptors, and on the modifying influence of the carbohydrate sidechains of these glycoconjugates. The biological role of host cell receptors in determining paramyxovirus adsorption and penetration of the cell will be defined.